The present invention relates to a method and apparatus for making unitary complex cores.
Cast metal parts are made by pouring molten metal into a two-piece mold consisting of a top portion, conventionally referred to as a cope, and a bottom portion conventionally referred to as a drag. Hollow metal parts are cast by forming a hollow cavity in the cast part by means of a core. The core is placed in the mold so that, as the molten metal is poured into the mold, the metal is displaced by the core and a cavity is thereby formed by the core within the cast metal part. Thus the core and the mold cooperate to define the cast metal part.
Prior art methods of producing a complex intricate core has consisted of manufacturing the core in sections, assembling the core sections and securing the sections together by means of glue. This prior art method is time consuming and expensive because the core sections had to be made individually and then assembled in a separate operation. The prior art method is also inaccurate as no two assemblies are put together in the same way.
In manufacturing double volute turbo charger housings, complex cores are required to form the intricate internal double volute cavity of the turbo charger housing. The core must be in the shape of a double volute in order to define the housing cavity when the turbo charger housing is cast. Prior art methods for manufacturing such complex cores have comprised forming two individual volutes and then assembling them into a core by means of gluing them together. As indicated above such prior art methods are unsatisfactory for the reasons given. Additional problems introduced by forming cores in sections is that this method may introduce dimensional inaccuracies in the cores. If the core dimensions vary from core to core, the metal parts cast with such cores will also have varying dimensions. In products such as double volute turbo charger housings, the dimensional tolerances of the internal double volute are exacting and should not vary since such variations would affect the performance characteristics of the turbo charger. Thus, it is desired to provide cores with close dimensional tolerances.
An additional problem which has been encountered in such double volute turbo charger housings which ma be caused by variation in core dimensions has been thermal cracking on the inside of the castings. When such cracks appear, turbo charger housings must be replaced. Turbo chargers are conventionally rebuilt after a certain number of hours or miles have been accumulated. If it is found, during such rebuilding, that the turbo charger housing is cracked, it cannot be reused and must be replaced. Thus, it is desirable to provide a core which eliminates thermal cracking of double volute turbo charger housings.